Evolutions of wireless network and wireless access method for cellular mobile communication (hereinafter referred to as “Long Term Evolution (LTE)” or “Evolved Universal Terrestrial Radio Access (EUTRA)”) have been specified in the Third Generation Partnership Project (3GPP). In LTE, as a method of wireless communication from a base station device to a mobile station device (downlink; hereinafter also denoted as “DL”), Orthogonal Frequency Division Multiplexing (OFDM), which is a multi-carrier transmission method, is used. Further, in LTE, as a method of communication from a mobile station device to the base station device (uplink, hereinafter also denoted as “UL”), SC-FDMA (Single-Carrier Frequency Division Multiple Access), which is a single-carrier transmission method, is used. In LTE, DFT-Spread OFDM (Discrete Fourier Transform-Spread OFDM) is used as a type of SC-FDMA.
In 3GPP, wireless network and wireless access method realizing data communication of higher speed (hereinafter referred to as “Long Term Evolution-Advanced (LTE-A)” or “Advanced Evolved Universal Terrestrial Radio Access (A-EUTRA)” utilizing wider frequency band than LTE have been considered. LTE-A must realize backward compatibility with LTE. LTE-A must satisfy the requirements that a base station device supporting LTE-A be capable of simultaneous communication with a mobile station device supporting LTE-A and a mobile station device supporting LTE, and that a mobile station device supporting LTE-A be capable of communication with a base station supporting LTE-A as well as a base station supporting LTE. In order to satisfy these requirements, LTE-A is supposed to support at least the same channel configuration as LTE.
A channel means a medium used for signal transmission. A channel used in a physical layer is referred to as a “physical channel,” and a channel used in a media access (Media Access Control: MAC) layer is referred to as a “logical channel.” There are various types of physical channels, including: Physical Downlink Shared CHannel (PDSCH) used for transmitting/receiving downlink data and control information; Physical Downlink Control CHannel (PDCCH) used for transmitting downlink control information; Physical Uplink Shared CHannel (PUSCH) used for transmitting/receiving uplink data and control information; Physical Uplink Control CHannel (PUCCH) used for transmitting/receiving control information; Synchronization CHannel (SCH) used for establishing downlink synchronization; Physical Random Access CHannel (PRACH) used for establishing uplink synchronization; and Physical Broadcast CHannel (PBCH) used for transmitting downlink system information. A mobile station device or a base station device places and transmits signals generated from control information and data on these physical channels.
Data transmitted through the physical downlink shared channel or the physical uplink shared channel is referred to as a “transport block.”
Control information placed on the physical uplink control channel is referred to as “Uplink Control Information” (UCI). The uplink control information may include (1) control information indicating an acknowledgement (ACK) or a negative acknowledgement (NACK) of receipt of data placed on the physical downlink shared channel (receipt acknowledgment; ACK/NACK), (2) control information indicating request for allocation of uplink resources (Scheduling Request: SR), and (3) control information indicating downlink reception quality (hereinafter also referred to as “channel quality”) (Channel Quality Indicator: CQI).
LTE-A proposes a technique of using a plurality of frequency bands of the same channel structure as LTE (hereinafter referred to as “component carrier: CC” or component frequency band) as one frequency band (wider frequency band) (this technique is referred to as “spectrum aggregation,” “carrier aggregation” or “frequency aggregation”). Specifically, in communication utilizing the carrier aggregation, each downlink component carrier (hereinafter also denoted as “DL CC”) transmits/receives a downlink physical channel, and each uplink component carrier (hereinafter also referred to as “UL CC”) transmits/receives an uplink physical channel. Namely, carrier aggregation is a technique allowing the base station and mobile station devices to simultaneously transmit/receive signals through a plurality of physical channels, using a plurality of component carriers.
In LTE-A, the coverage for communication by a base station device using one frequency band is referred to as a “cell.” Carrier aggregation represents communication using a plurality of cells using a plurality of frequency bands, and hence, it is also referred to as “cell aggregation.” In cell aggregation, a plurality of cells are defined as either one of two different types of cells. Specifically, one cell is defined as a primary cell (Pcell), and other cells are defined as secondary cells (Scell). A base station device independently sets the primary and secondary cells for each mobile station device where cell aggregation is adopted.
A primary cell is always configured with a set (combination) of one downlink component carrier and one uplink component carrier. A secondary cell is configured with at least one downlink component carrier, and it may or may not be configured with an uplink component carrier. The component carrier used in the primary cell is referred to as a “primary component carrier (PCC).” The component carrier used in the secondary cell is referred to as a “secondary component carrier (SCC).” In the primary and secondary cells, data communication using physical downlink shared channel and physical uplink shared channel is executed commonly, while various other processes are executed independently.
Briefly stated, a plurality of processes are executed only by the primary cell and not by the secondary cell or cells. By way of example, acquisition of system information and determination of radio link failure (RLF) are executed on the downlink, and execution of random access procedure using physical random access channel and transmission/reception of uplink control information using physical uplink control channel are executed on the uplink, of the primary cell. Basically, all processes that are executed in LTE without using cell aggregation are done by the primary cell, while processes other than data communication are not executed by the secondary cell.
A mobile station device transmits control information (receipt acknowledgement) indicating either a positive or negative acknowledgment of the data received through a physical downlink shared channel, using a physical uplink control channel. Based on the receipt acknowledgement received from the mobile station device, the base station device controls re-transmission of data that has been transmitted to the mobile station device, using the physical downlink shared channel. In LTE-A using cell aggregation, the base station device can transmit data to mobile station devices using a plurality of physical downlink shared channels at one time. The mobile station device that has received data through the plurality of physical downlink shared channels with cell aggregation must send a plurality of receipt acknowledgements to the base station device at one time. According to LTE, a base station device can transmit data to a mobile station device using only one physical downlink shared channel at one time, and the mobile station device that has received the data through one physical downlink shared channel sends one receipt acknowledgement to the base station device using the physical uplink control channel. In LTE-A, a new method of transmission has been studied to enable the mobile station device to send a plurality of receipt acknowledgements to the base station device (Non-Patent Literature 1).
More specifically, a method of transmission (ACK/NACK channel selection, PUCCH format 1b with channel selection) is under review as a new method of transmission, in which implicit receipt acknowledgement information is provided by the mobile station device selecting a resource of physical uplink control channel used for signal transmission from among a plurality of candidate resources of physical uplink control channel, in accordance with the receipt acknowledgement information and, in addition, explicit receipt acknowledgement information is provided by the mobile station device transmitting a modulated signal on the physical uplink control channel using the selected resource. The mobile station device determines the candidate resources used for resource selection of physical uplink control channel based on the detected physical downlink control channel.
According to LTE, resource allocation of physical uplink control channel used for transmitting receipt acknowledgement is implicitly carried out based on the resources used for the physical downlink control channel. Such resource allocation is referred to as “implicit resource allocation.” The “implicit resource allocation” means that information dedicated for resource allocation is not used, and resource allocation is done using pieces of information intended for other purposes. On the other hand, “explicit resource allocation” means that resource allocation is done using information dedicated only for resource allocation.
The physical downlink control channel consists of a plurality of control channel elements (hereinafter also denoted as “CCEs”). The control channel element is a unit of resources used for the physical downlink control channel. A corresponding relation between the resources of the physical uplink control channel used for transmitting receipt acknowledgement and the control channel elements is established in advance. CCEs used between a base station device and a mobile station device have numbers allocated to identify respective CCEs. Numbering of CCEs is done in accordance with a predetermined rule.
The physical downlink control channel consists of an aggregated plurality of CCEs (CCE aggregation). The number of CCEs forming the aggregation will be hereinafter referred to as “CCE aggregation number.” The CCE aggregation number forming a physical downlink control channel is set by the base station device in accordance with code rate set for the physical downlink control channel and the number of bits of control information carried on the physical downlink control channel. By way of example, the base station device may form a physical downlink control channel using one CCE, may form a physical downlink control channel using two CCEs, may form a physical downlink control channel using four CCEs, or may form a physical downlink control channel using eight CCEs. Typically, for a mobile station device with good channel quality, the base station device forms a physical downlink channel using a smaller number of CCEs, and for a mobile station device with poor channel quality, the base station device forms a physical downlink control channel using a larger number of CCEs. Further, for transmitting control information of smaller number of bits, the base station device forms a physical downlink control channel using a smaller number of CCEs, and for transmitting control information of larger number of bits, it forms a physical downlink control channel using a larger number of CCEs.
The physical uplink control channel used for transmitting the receipt acknowledgement is constituted of three-dimensional resources, including physical resource blocks as resources defined in frequency domain and time domain, a frequency domain code and a time domain code. Various combinations of resources of physical uplink control channel used for transmitting receipt acknowledgement in the communication system have numbers allocated thereto, for identifying each of the combinations of resources, based on a predetermined rule.
By way of example, a corresponding relation between the numbers of CCEs and the numbers of resources for the physical uplink control channel used for transmitting receipt acknowledgement is established in advance, and a CCE and a resource for the physical uplink control channel having the same number are related to each other. The mobile station device uses the resource of physical uplink control channel having the number corresponding to the CCE having the smallest number among CCEs used for the physical downlink control channel, from which control information addressed to the mobile station device itself is detected, to transmit the receipt acknowledgement for the data of the physical downlink shared channel, resource allocation of which is indicated by the physical downlink control channel. Similar to the mobile station device, the base station device recognizes the corresponding relation between the CCE numbers and the numbers of resources for the physical uplink control channel used for transmitting receipt acknowledgement, and it allocates CCEs used for the physical downlink control channel in consideration of resources allocated to the physical uplink control channel of the mobile station device. Specifically, based on the CCE used for the physical downlink control channel from which control information addressed to the mobile station device itself is detected, the mobile station device recognizes the resource for the physical uplink control channel used for transmitting the receipt acknowledgement allocated to the device itself.
In LTE-A using cell aggregation, a method of allocating candidate resources for the physical uplink control channel corresponding to the new transmission method has been studied, in connection with the receipt acknowledgement (Non-Patent Literature 2). In the following, allocation of candidate resources used for resource selection of the physical uplink control channel, when receipt acknowledgement is transmitted using ACK/NACK channel selection, which is under review, will be described. Consider transmission of the physical downlink control channel in a primary cell. As in LTE, resources of the physical uplink control channel having the corresponding relation to the CCEs of physical downlink control channel are allocated to the mobile station device as candidate resources in implicit manner. When the physical downlink control channel is transmitted in a primary cell, information related to resource allocation included in the physical downlink control channel indicates the resources of physical downlink shared channel of the primary cell or a secondary cell.
If the physical downlink control channel is transmitted in a secondary cell, different from LTE, a resource of the physical uplink control channel is allocated to a mobile station device as a candidate resource in an explicit manner using prescribed signaling. As the prescribed signaling, a method of explicitly allocating candidate resources of physical uplink control channel using RRC (Radio Resource Control) signaling, and a method of explicitly allocating candidate resources of physical uplink control channel using control information of the physical downlink control channel have been considered.
In the method of explicitly allocating the candidate resources of physical uplink control channel using RRC signaling, before starting data communication with cell aggregation, candidate resources for the physical uplink control channel are already allocated to the mobile station device. When the mobile station device detects a physical downlink control channel in a secondary cell, in other words, when it recognizes transmission of the physical downlink control channel in a secondary cell, it uses a resource of the physical uplink control channel allocated in advance by RRC signaling, as the candidate resource used for selecting a physical uplink control channel for implicitly indicating the information of receipt acknowledgement.
In the method in which candidate resources of physical uplink control channel are explicitly allocated using control information of the physical downlink control channel, upon detection of the physical downlink control channel in a secondary cell, a mobile station device uses a resource of the physical uplink control channel indicated by the control information of the physical downlink control channel detected in the secondary cell, as the candidate resource used for selection of the physical uplink control channel for implicitly indicating the information of receipt acknowledgement. In the method in which candidate resources of the physical uplink control channel are explicitly allocated using the control information of physical downlink control channel, a plurality of potential candidate resources for the physical uplink control channel are allocated in advance to the mobile station device by RRC signaling, and using the control information of physical downlink control channel, one of the plurality of potential candidate resources set by the RRC signaling is indicated.
As to the control information indicating the candidate resources for the physical uplink control channel included in the physical downlink control channel, control information generally used for other purposes may be utilized. Here, the control information is utilized such that in a first situation, a control information field is interpreted as a first piece of control information, in a second situation, the control information field is interpreted as a second piece of control information, the first situation is different from the second situation, and the first piece of control information is different from the second piece of control information. By way of example, if the physical downlink control channel is transmitted in a primary cell, a control information field may be interpreted as a piece of information indicating a transmit power control value of a physical uplink control channel. If the physical downlink control channel is transmitted in a secondary cell, the control information field mentioned above may be interpreted as a piece of control information indicating candidate resources used for selecting a physical uplink control channel, selected for implicitly indicating the information of receipt acknowledgement.
In LTE-A, for transmitting receipt acknowledgement, linear control of transmit power in accordance with the number of transport blocks received by a plurality of physical downlink shared channels has been considered.
Further, in LTE-A, application of time domain bundling to ACK/NACK channel selection has been considered (Non-Patent Literature 3). In TDD (Time Division Duplex), a mobile station device transmits, using a single uplink subframe, a receipt acknowledgement for the data of a plurality of downlink subframes received using a physical downlink shared cannel. Here, execution of a logical multiplication by the mobile station device on a plurality of receipt acknowledgements for the data received in a plurality of subframes is referred to as “time domain bundling.” ACK/NACK bundling refers to a process executed by a mobile station device, of performing a logical multiplication on a plurality of receipt acknowledgements and thereby generating a piece of information having smaller number of bits (for example, 1 bit) than the information before execution of the multiplication. By way of example, if the plurality of receipt acknowledgements are all positive, the mobile station device generates one positive acknowledgement as a result of logical multiplication, and transmits it to the base station device. If one negative acknowledgement is included among the plurality of receipt acknowledgements, the mobile station device generates a negative acknowledgement as a result of logical multiplication, and transmits it to the base station device.
The mobile station device transmits the receipt acknowledgement as a result of logical multiplication of the receipt acknowledgements for the data of a plurality of downlink subframes to the base station device through the physical uplink control channel. Using cell aggregation, the mobile station device applies time domain bundling for the receipt acknowledgements for data of a plurality of subframes of each cell, selects a resource for the physical uplink control channel used for transmitting a signal in accordance with the information of a plurality of receipt acknowledgements of a plurality of cells on which logical multiplication has been executed, and using the selected resource, transmits a modulated signal.
The mobile station device determines candidate resources used for resource selection for the physical uplink control channel, based on the physical downlink control channel detected in the subframe to which data is allocated most recently, in each cell.
For a cell to which candidate resources are implicitly allocated, resources corresponding to the CCE used for the physical downlink control channel corresponding to the data detected in the subframe to which the data has been allocated most recently in the cell, is determined by the mobile station device to be the candidate resources, and the thus determined resources are used for the resource selection process for the physical uplink control channel.
For a cell to which candidate resources are explicitly allocated, resources indicated by the control information of the physical downlink control channel corresponding to the data detected in the subframe to which the data has been allocated most recently in the cell, are determined by the mobile station device to be the candidate resources, and the thus determined resources are used for the resource selection process for the physical uplink control channel. Alternatively, for a cell to which candidate resources are explicitly allocated, resources allocated in advance by RRC signaling to the physical downlink control channel corresponding to the data detected in the subframe to which the data has been allocated most recently in the cell, are determined by the mobile station device to be the candidate resources, and the thus determined resources are used for the resource selection process for the physical uplink control channel.
Further, in LTE-A, application of spatial bundling to ACK/NACK channel selection has been considered. In LTE-A, it has been proposed that a base station device applies MIMO (Multi-Input Multi-Output) spatial multiplexing, so that a plurality of data are subjected to spatial multiplexing using one physical downlink shared channel, and signals containing a plurality of spatially-multiplexed data are transmitted to a mobile station device. The mobile station device transmits receipt acknowledgements for the plurality of spatially-multiplexed data on the physical downlink shared channel, through the uplink. Here, execution of the logical multiplication on the plurality of receipt acknowledgements for the data received through one same physical downlink shared channel by the mobile station device is referred to as “spatial bundling.” The mobile station device transmits the receipt acknowledgement as a result of logical multiplication to the base station device through the physical uplink control channel.